The frogs in my neighbour's pond vanished three years ago. My neighbour
said a heron and kingfish ate them all. Could there be other causes
and is the pond likely to get repopulated?

Phil Bishop, a zoologist at Otago University, responded.

Disappearing frog populations have been documented since the early 1990s
and we now realise that this is a real problem rather than simply fluctuating
populations. In 2000 a frog disease caused by a fungus (a chytrid fungus)
was identified in a pond in Christchurch and this has been suspected to have
caused many populations to disappear around New Zealand, including native
frogs on the North Island. The southern most point that the disease has been
positively identified is Cave, so it may not have travelled as far south as Dunedin yet.

However, many people in the Otago region have reported frog declines in the
last ten years, and now many populations seem to be in the recovery phase,
so it is possible that the disease-front moved through the Dunedin area and
we have not yet identified it from that region.

There are other reasons that may explain why the frogs disappeared.
Many mammalian predators (e.g. feral or domestic cats, hedgehogs, ferrets)
like to eat (or play with) the brown tree frogs and herons and kingfishers include
them in their diet. Other diseases such as those caused by other fungi or Rana
virus may attack frog populations that are under stress from a changing
environment and cause the local populations to become extinct. Ponds
act as localised sources of frogs and there will be many others in the
surrounding vegetation, so if the pond-dwelling frogs are wiped out by
predators or disease then it is likely that the population will slowly
re-establish itself.

2008 was recognised as the Global Year of the Frog to raise awareness
of the frog extinction crisis and to get people to help.
For more information see www.nzfrogs.org.